Interspecific temporal and spatial differences in the acquisition of litter-derived nitrogen by ectomycorrhizal...

The spatiotemporal dynamics of, and interspecific differences in, the acquisition of litter-derived nitrogen (N) by natural assemblages of ectomycorrhizal root tips are poorly understood. Small cylindrical mesh bags containing (15)N-labelled beech (Fagus sylvatica) leaf litter that permit hyphal but not root ingrowth were inserted vertically into the top soil layer of an old-growth beech forest. The lateral transfer of (15)N into the circumjacent soil, roots, microbes and ectomycorrhizas was measured during an 18-month exposure period. Ectomycorrhial fungi (EMF) showed large interspecific variation in the temporal pattern and extent of (15)N accumulation. Initially, when N was mainly available from the leachate, microbes were more efficient at N immobilization than the majority of EMF, but distinct fungal species also showed significant (15)N accumulation. During later phases, the enrichment of (15)N in Tomentella badia was higher than in microbes and other EMF species. Roots and soil accumulated (15)N with a large delay compared with microbes and EMF. Because approximately half of the studied fungal species had direct access to N from leaf litter and the remainder to N from leached compounds, we suggest that EMF diversity facilitates the N utilization of the host by capturing N originating from early-released solutes and late degradation products from a recalcitrant source.